invoke.texi

早期freebsd实现

the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.

Unrecognized input files, not requiring compilation or assembly, are
ignored.

@item -S
Stop after the stage of compilation proper; do not assemble.  The output
is in the form of an assembler code file for each non-assembler input
file specified.

By default, the assembler file name for a source file is made by
replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.

Input files that don't require compilation are ignored.

@item -E
Stop after the preprocessing stage; do not run the compiler proper.  The
output is in the form of preprocessed source code, which is sent to the
standard output.

Input files which don't require preprocessing are ignored.

@cindex output file option
@item -o @var{file}
Place output in file @var{file}.  This applies regardless to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.

Since only one output file can be specified, it does not make sense to
use @samp{-o} when compiling more than one input file, unless you are
producing an executable file as output.

If @samp{-o} is not specified, the default is to put an executable file
in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
@file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
all preprocessed C source on standard output.@refill

@item -v
Print (on standard error output) the commands executed to run the stages
of compilation.  Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.

@item -pipe
Use pipes rather than temporary files for communication between the
various stages of compilation.  This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
no trouble.
@end table

@node Dialect Options
@section Options Controlling Dialect
@cindex dialect options
@cindex language dialect options
@cindex options, dialect

The following options control the dialect of C or C++ that the compiler
accepts:

@table @code
@cindex ANSI support
@item -ansi
Support all ANSI standard C programs.

This turns off certain features of GNU C that are incompatible with ANSI
C, such as the @code{asm}, @code{inline} and @code{typeof} keywords, and
predefined macros such as @code{unix} and @code{vax} that identify the
type of system you are using.  It also enables the undesirable and
rarely used ANSI trigraph feature, and disallows @samp{$} as part of
identifiers.

The alternate keywords @code{__asm__}, @code{__extension__},
@code{__inline__} and @code{__typeof__} continue to work despite
@samp{-ansi}.  You would not want to use them in an ANSI C program, of
course, but it useful to put them in header files that might be included
in compilations done with @samp{-ansi}.  Alternate predefined macros
such as @code{__unix__} and @code{__vax__} are also available, with or
without @samp{-ansi}.

The @samp{-ansi} option does not cause non-ANSI programs to be
rejected gratuitously.  For that, @samp{-pedantic} is required in
addition to @samp{-ansi}.  @xref{Warning Options}.

The macro @code{__STRICT_ANSI__} is predefined when the @samp{-ansi}
option is used.  Some header files may notice this macro and refrain
from declaring certain functions or defining certain macros that the
ANSI standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.

The functions @code{alloca}, @code{abort}, @code{exit}, and
@code{_exit} are not builtin functions when @samp{-ansi} is used.

@item -fall-virtual
Treat certain member functions as virtual, implicitly (C++ only).  This
applies to all member functions declared in the same class with a
``method-call'' operator method (except for constructor functions and
@code{new} or @code{delete} member operators).  In effect, all of these
methods become ``implicitly virtual.''

This does not mean that all calls to these methods will be made through
the internal table of virtual functions.  There are some circumstances
under which it is obvious that a call to a given virtual function can be
made directly, and in these cases the calls still go direct.

The effect of making all methods of a class with a declared
@samp{operator->()()} implicitly virtual using @samp{-fall-virtual}
extends also to all non-constructor methods of any class derived from
such a class.

@item -fdollars-in-identifiers
Permit the use of @samp{$} in identifiers (C++ only).  You can also use
@samp{-fno-dollars-in-identifiers} to explicitly prohibit use of
@samp{$}.  (GNU C++ allows @samp{$} by default on some target systems
but not others.)

@item -fenum-int-equiv
Permit implicit conversion of @code{int} to enumeration types (C++
only).  Normally GNU C++ allows conversion of @code{enum} to @code{int},
but not the other way around.

@item -fno-asm
Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
keyword.  These words may then be used as identifiers.  You can
use @code{__asm__}, @code{__inline__} and @code{__typeof__} instead.
@samp{-ansi} implies @samp{-fno-asm}.

@item -fno-builtin
Don't recognize built-in functions that do not begin with two leading
underscores. Currently, the functions affected include @code{_exit},
@code{abort}, @code{abs}, @code{alloca}, @code{cos}, @code{exit},
@code{fabs}, @code{labs}, @code{memcmp}, @code{memcpy}, @code{sin},
@code{sqrt}, @code{strcmp}, @code{strcpy}, and @code{strlen}.

The @samp{-ansi} option prevents @code{alloca} and @code{_exit} from
being builtin functions.

@item -fno-strict-prototype
Treat a function declaration with no arguments, such as @samp{int foo
();}, as C would treat it---as saying nothing about the number of
arguments or their types (C++ only).  Normally, such a declaration in
C++ means that the function @code{foo} takes no arguments.

@item -fthis-is-variable
Permit assignment to @code{this} (C++ only).  The incorporation of
user-defined free store management into C++ has made assignment to
@samp{this} an anachronism.  Therefore, by default it is invalid to
assign to @code{this} within a class member function.  However, for
backwards compatibility, you can make it valid with
@samp{-fthis-is-variable}.

@item -trigraphs
Support ANSI C trigraphs.  You don't want to know about this
brain-damage.  The @samp{-ansi} option implies @samp{-trigraphs}.

@cindex traditional C language
@cindex C language, traditional
@item -traditional
Attempt to support some aspects of traditional C compilers.
Specifically:

@itemize @bullet
@item
All @code{extern} declarations take effect globally even if they
are written inside of a function definition.  This includes implicit
declarations of functions.

@item
The keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
and @code{volatile} are not recognized.  (You can still use the
alternative keywords such as @code{__typeof__}, @code{__inline__}, and
so on.)

@item
Comparisons between pointers and integers are always allowed.

@item
Integer types @code{unsigned short} and @code{unsigned char} promote
to @code{unsigned int}.

@item
Out-of-range floating point literals are not an error.

@item
String ``constants'' are not necessarily constant; they are stored in
writable space, and identical looking constants are allocated
separately.  (This is the same as the effect of
@samp{-fwritable-strings}.)

@cindex @code{longjmp} and automatic variables
@item
All automatic variables not declared @code{register} are preserved by
@code{longjmp}.  Ordinarily, GNU C follows ANSI C: automatic variables
not declared @code{volatile} may be clobbered.

@item
In the preprocessor, comments convert to nothing at all, rather than
to a space.  This allows traditional token concatenation.

@item
In the preprocessor, macro arguments are recognized within string
constants in a macro definition (and their values are stringified,
though without additional quote marks, when they appear in such a
context).  The preprocessor always considers a string constant to end
at a newline.

@item
The predefined macro @code{__STDC__} is not defined when you use
@samp{-traditional}, but @code{__GNUC__} is (since the GNU extensions
which @code{__GNUC__} indicates are not affected by
@samp{-traditional}).  If you need to write header files that work
differently depending on whether @samp{-traditional} is in use, by
testing both of these predefined macros you can distinguish four
situations: GNU C, traditional GNU C, other ANSI C compilers, and
other old C compilers.
@end itemize

You may wish to use @samp{-fno-builtin} as well as @samp{-traditional}
if your program uses names that are normally GNU C builtin functions for
other purposes of its own.

@item -traditional-cpp
Attempt to support some aspects of traditional C preprocessors.
This includes the last three items in the table immediately above,
but none of the other effects of @samp{-traditional}.

@item -fcond-mismatch
Allow conditional expressions with mismatched types in the second and
third arguments.  The value of such an expression is void.

@item -funsigned-char
Let the type @code{char} be unsigned, like @code{unsigned char}.

Each kind of machine has a default for what @code{char} should
be.  It is either like @code{unsigned char} by default or like
@code{signed char} by default.

Ideally, a portable program should always use @code{signed char} or
@code{unsigned char} when it depends on the signedness of an object.
But many programs have been written to use plain @code{char} and
expect it to be signed, or expect it to be unsigned, depending on the
machines they were written for.  This option, and its inverse, let you
make such a program work with the opposite default.

The type @code{char} is always a distinct type from each of
@code{signed char} or @code{unsigned char}, even though its behavior
is always just like one of those two.

@item -fsigned-char
Let the type @code{char} be signed, like @code{signed char}.

Note that this is equivalent to @samp{-fno-unsigned-char}, which is
the negative form of @samp{-funsigned-char}.  Likewise,
@samp{-fno-signed-char} is equivalent to @samp{-funsigned-char}.

@item -fsigned-bitfields
@itemx -funsigned-bitfields
@itemx -fno-signed-bitfields
@itemx -fno-unsigned-bitfields
These options control whether a bitfield is signed or unsigned, when the
declaration does not use either @code{signed} or @code{unsigned}.  By
default, such a bitfield is signed, because this is consistent: the
basic integer types such as @code{int} are signed types.

However, when @samp{-traditional} is used, bitfields are all unsigned
no matter what.

@item -fwritable-strings
Store string constants in the writable data segment and don't uniquize
them.  This is for compatibility with old programs which assume they
can write into string constants.  @samp{-traditional} also has this
effect.

Writing into string constants is a very bad idea; ``constants'' should
be constant.
@end table

@node Warning Options
@section Options to Request or Suppress Warnings
@cindex options to control warnings
@cindex warning messages
@cindex messages, warning
@cindex suppressing warnings

Warnings are diagnostic messages that report constructions which
are not inherently erroneous but which are risky or suggest there
may have been an error.

You can request many specific warnings with options beginning @samp{-W},
for example @samp{-Wimplicit} to request warnings on implicit
declarations.  Each of these specific warning options also has a
negative form beginning @samp{-Wno-} to turn off warnings;
for example, @samp{-Wno-implicit}.  This manual lists only one of the
two forms, whichever is not the default.

These options control the amount and kinds of warnings produced by GNU
CC:

@table @code
@cindex syntax checking
@item -fsyntax-only
Check the code for syntax errors, but don't emit any output.

@item -w
Inhibit all warning messages.

@item -Wno-import
Inhibit warning messages about the use of @samp{#import}.

@item -pedantic
Issue all the warnings demanded by strict ANSI standard C; reject
all programs that use forbidden extensions.  

Valid ANSI standard C programs should compile properly with or without
this option (though a rare few will require @samp{-ansi}).  However,
without this option, certain GNU extensions and traditional C features
are supported as well.  With this option, they are rejected.

@samp{-pedantic} does not cause warning messages for use of the
alternate keywords whose names begin and end with @samp{__}.  Pedantic
warnings are also disabled in the expression that follows
@code{__extension__}.  However, only system header files should use
these escape routes; application programs should avoid them.
@xref{Alternate Keywords}.

This option is not intended to be @i{useful}; it exists only to satisfy
pedants who would otherwise claim that GNU CC fails to support the ANSI
standard.

Some users try to use @samp{-pedantic} to check programs for strict ANSI
C conformance.  They soon find that it does not do quite what they want:
it finds some non-ANSI practices, but not all---only those for which
ANSI C @emph{requires} a diagnostic.

A feature to report any failure to conform to ANSI C might be useful in
some instances, but would require considerable additional work and would
be quite different from @samp{-pedantic}.  We recommend, rather, that
users take advantage of the extensions of GNU C and disregard the
limitations of other compilers.  Aside from certain supercomputers and
obsolete small machines, there is less and less reason ever to use any
other C compiler other than for bootstrapping GNU CC.

@item -pedantic-errors
Like @samp{-pedantic}, except that errors are produced rather than
warnings.

@item -W
Print extra warning messages for these events: